One of the recurring questions developers ask me at conferences is “What’s the best way to add Kotlin to my existing Android app?” If you work in a team with more than a handful of people, adopting a new language can become complex. Over time, my answer has become longer and I’ve fine-tuned it based on my own experiences adding Kotlin to existing projects, and speaking with others — both at Google and the external developer community — about their journeys.

Here’s a guide to help you successfully introduce Kotlin to existing projects on larger teams. Many teams within Google, including the Android Developer Relations team, have used these techniques successfully. Two notable examples are the 2018 Google I/O app, which was rewritten completely in Kotlin, and Plaid, which has a mix of Java and Kotlin.